Devices and methods for cellular communication

ABSTRACT

A method in a network component for use in a cellular network comprises transmitting handover information from the network component to a mobile device. The handover information comprises information including information of a plurality of target cells with which the mobile device may subsequently communicate. A corresponding method in a mobile device is also provided.

TECHNICAL FIELD

The embodiments disclosed herein relate to devices and methods for usein cellular communication. In an exemplary embodiment, the embodimentsrelate to devices and methods which provide for improved handover fromone cell to another in a cellular network. For example, the embodimentsinvolve the transmission and/or receipt of handover information, whichincludes information of a plurality of target cells designated aspossible targets for handover.

BACKGROUND

A cellular network used by a mobile device may cover an entire landmass,but will certainly extend over many thousands of square kilometres.However, since a single cellular network base station has, at the most,a maximum range of only a few tens of kilometres, and possibly less, itis necessary for a mobile device to be able to communicate with aplurality of base stations, and to cease communication with one cell(henceforth the ‘source cell’) and commence communication with anothercell (henceforth the ‘target cell’) as the mobile device moves betweenthe land areas served by those cells.

As the mobile device changes the cell used for communication, it mustcease operating using the communication particulars of the source celland commence communication using the communication particulars of thetarget cell. During this changeover, it is desirable for communicationto continue unimpeded. In particular, it is preferred that voice callsand data sessions are not interrupted, delayed or lost during thechangeover.

The changeover between cells is managed by a ‘handover procedure’. Toestablish uniformity between multiple network operators and handsetproviders, the handover procedure is defined according to a set ofstandards. In respect of cellular networks serving some current andfuture mobile devices, certain relevant standards are set out indocuments published by the body known as the 3rd Generation PartnershipProject (3GPP). Several of these are available on the internet(http://www.3gpp.org), and are listed below:

-   -   TS36.214—“3rd Generation Partnership Project; Technical        Specification Group Radio Access Network; Evolved Universal        Terrestrial Radio Access (E-UTRA); Physical layer measurements        (Release 8)”, V8.7.0, September 2009;    -   TS36.331—“3rd Generation Partnership Project; Technical        Specification Group Radio Access Network; Evolved Universal        Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC);        Protocol specification (Release 8)”, V8.7.0, September 2009;    -   TS36.133—“3rd Generation Partnership Project; Technical        Specification Group Radio Access Network; Evolved Universal        Terrestrial Radio Access (E-UTRA); Requirements for support of        radio resource management”, V8.7.0, September 2009;    -   TS36.304—“3rd Generation Partnership Project; Technical        Specification Group Radio Access Network; Evolved Universal        Terrestrial Radio Access (E-UTRA); User Equipment (UE)        procedures in idle mode”, V8.7.0, September 2009; and    -   TS36.423—“3rd Generation Partnership Project; Technical        Specification Group Radio Access Network; Evolved Universal        Terrestrial Radio Access (E-UTRA); X2 application protocol        (X2AP)”, V10.5.0, March. 2012.

This disclosure relates to improved handover and reestablishmentprocedures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure and the embodiments set out herein can be betterunderstood with reference to the description of the embodiments set outbelow, in conjunction with the appended drawings wherein:

FIG. 1 is a diagram of an exemplary cellular network with a plurality ofcells, base stations, mobile management entities and mobile devices;

FIG. 2 is a schematic of an exemplary base station for use in thecellular network of FIG. 1;

FIG. 3 is a schematic of an exemplary mobile device for use in thecellular network of FIG. 1;

FIG. 4 is a schematic of an exemplary mobile management entity for usein the cellular network of FIG. 1;

FIG. 5 is a plot of a first simulation showing the positions of aplurality of mobile devices with respect to a cell to which they areconnected and its neighbouring cells;

FIG. 6 is a plot of a second simulation showing the positions of aplurality of mobile devices with respect to a cell to which they areconnected and its neighbouring cells;

FIG. 7 is a flow diagram illustrating a first exemplary method forperforming a handover operation with a plurality of target cells;

FIG. 8 is a flow diagram illustrating a second exemplary method forperforming a handover operation with a plurality of target cells;

FIG. 9 is a diagram of an exemplary cellular network with a plurality ofcells, base stations, mobile management entities and mobile devices;

FIG. 10 is a flow chart of an exemplary method performed by a mobiledevice for performing handover and reestablishment procedures;

FIGS. 11A, 12A and 13A are flow charts of exemplary methods performed bya network component for performing a handover procedure; and

FIGS. 11B, 12B and 13B are flow charts of exemplary methods performed bya mobile device for performing a handover procedure.

DETAILED DESCRIPTION

A wireless cellular communications network 1000 is a system forcommunicating with mobile devices 110 a-110 c across generally largedistances such as over an entire landmass. Of course, cellular networksmay also be smaller, but in any event are established by a plurality offixed-location radio frequency transceivers known as base stations 102a-102 g. Each base station 102 a-102 g is able to communicate withmobile devices 110 a-110 c wirelessly in the megahertz (MHz) and/or lowgigahertz (GHz) radio frequency ranges, and up to a distance of a fewtens of kilometres, although other ranges are possible.

Base stations 102 a-102 g may be spread across an area of land in such away so as to provide complete network coverage; that is, to enable amobile device 110 a-110 c to wirelessly access at least one base station102 a-102 g wherever it is located in the area of land served by thebase stations 102 a-102 g. Of course, cellular networks may exist whichdepart from this scenario and often coverage may be incomplete. Acellular network 1000 may be established by dividing an area served bythe network into a plurality of adjacent areas called ‘cells’ 100 a-100e. Each cell 100 a-100 e may be served by at least one base station 102a-102 g. Base stations may serve more than one cell. Conventionally,cells may be represented as regular shapes, usually hexagonal, sincethis allows for convenient cell tessellation. However, cells may be anyshape, regular or irregular, depending on the preferred implementationand factors such as, for example, signal characteristics, signalinterference, geography, climatic conditions, or buildings or otherstructures within the cell.

An example of a cellular network 1000 is shown in FIG. 1. Here fivecells 100 a-100 e are shown, each served by at least one base-station102 a-102 g. One of the cells, 100 c, illustrated is served by two basestations 102 c, 102 g. Moreover, one of the base stations, 102 f,illustrated serves three cells 102 a, 102 b and 102 d. The skilledperson will appreciate that the illustrated cellular network is a highlysimplified example which illustrates the principle, and more complexarrangements of cells and base stations are possible.

Base stations may communicate with each other directly or they maycommunicate with each other indirectly via a mobile management entity(MME) 104 a, 104 b, or both. In the illustrated arrangement, basestations 102 b and 102 c, for instance, communicate with each otherdirectly, for example using an ‘X2 link’ 106. Base stations 102 a, 102 band 102 f communicate with each other indirectly via MME 104 a, forexample using an ‘S1 interface’ 108.

As shown, at least some of the base stations are in communication withmobile devices 110 a-110 c. In particular, base station 102 f is inwireless communication with mobile device 110 a via cell 100 a; basestation 102 b is in wireless communication with mobile device 110 b viacell 100 b; and base station 102 g is in wireless communication withmobile device 110 c via cell 100 c.

A schematic of a base station 200 is shown in FIG. 2. The base station200 comprises a network component 202 comprising a processing unit 204,a first communications port 206 for communicating directly with anotherbase station, for instance using an ‘X2 link’, and a secondcommunications port 208 for communicating indirectly with another basestation, for instance using an ‘S1 interface’. The base stationcomprises a radio frequency (RF) transceiver 210 connected to an antenna212 for communicating wirelessly with a plurality of mobile devices. Thebase station comprises a memory 214 connected to the processing unit 204and adapted to execute computer readable instructions described in moredetail below.

A schematic of a mobile management entity (MME) 400 is shown in FIG. 4.The MME comprises a processing unit 402 connected to a series ofcommunications ports 404 a-404 c for communicating with base stations,for instance using an ‘S1 interface’.

Each cell 100 a-100 e may be assigned a variety of communicationparticulars, including a plurality of frequencies over which the mobiledevice and base station 102 a-102 g can communicate, a particularbandwidth, a ‘cell radio network temporary identifier’ (C-RNTI) and a‘random access channel’ (RACH) configuration. More or fewercommunication particulars are also possible, and each cell 100 a-100 emay be assigned one or more of the communication particulars. Adjacentcells 100 a-100 d may use different frequencies over which the mobiledevice and base station can communicate. However, this is not essential.Adjacent or neighbouring cells 100 a-100 e may use the same or differentbandwidths, physical control channel configuration parameters, forexample random access channel configuration parameters. For the purposesof this description, an adjacent cell is immediately adjacent, partiallyor wholly contained within, or partially or wholly overlapping anothercell; whereas a neighbouring cell is close enough such that it ispossible for a mobile device to receive signals from both cells. In FIG.1, cells 102 a and 102 d are adjacent, for example, whereas cells 102 band 102 e are neighbouring, because a mobile device located midwaybetween the two could well receive signals from both (as well as fromcells 102 a and 102 d).

For simplicity and in accordance with convention, the remainingdescription assumes a network of hexagonal cells, each cell served by asingle base station located in the centre of the cell. However, this ispurely for illustration and the scope of the appended claims is notlimited to this simplified arrangement and may be implemented using anyappropriate arrangement of cells and base stations. Moreover, whilst amobile device may communicate with (or is ‘served by’) a base station(specifically a network component of that base-station), for concisenessthe remaining description may refer to a mobile device communicatingwith or being ‘served by’ a cell. Likewise, the remaining descriptionmay refer to communication between a base station or network componentor mobile device ‘via’ a cell. Wherever this language is used, it willbe understood that what is meant is that the mobile device communicateswith a base station or network component using the communicationparticulars provided for according to that cell.

A mobile device 110 a-110 e may be adapted to change the cell 100 a-100e it uses for communication as it moves about in an area served by thecellular network 1000. The mobile device may cease operating using thecommunication particulars of its source cell and may commencecommunication using the communication particulars of a new target cell.This changeover between cells is called ‘handover’ and may be managed bya ‘handover procedure’. As explained above, an existing handoverprocedure may be defined according to a set of standards, some of whichare listed above. Of course, whilst adherence to standards is preferred,it is not essential.

A schematic of a mobile device 300 is shown in FIG. 3. The mobile device300 comprises a processing unit 302 and radio frequency (RF) transceiver304 connected to an antenna 306 for communicating wirelessly with aplurality of base-stations. The mobile device comprises a memory 308connected to the processing unit 302 and adapted to execute computerreadable instructions described in more detail below

In summary, one existing handover process operates as follows. Thisexample will be based on mobile device 110 a communicating with a sourcebase station 102 f via source cell 100 a, however the skilled personwill appreciate that other examples are possible. In accordance with thestandards set out in TS36.214, a mobile device 110 a periodically takesa set of measurements of the strength of signals received from thesource cell 100 a and any cells 100 b-100 e neighbouring the source celland creates a report detailing the measurements. As explainedpreviously, for the purposes of this description “neighbouring” does notnecessarily mean immediately adjacent, but includes cells which areclose enough to the source cell to transmit signals which are receivedby the mobile device. The report is sent to the source cell 100 a forprocessing by the network processors in source base station 102 f. Basedon the report sent by the mobile device 110 a, the network processorswill establish which cell the mobile device should communicate with. Forexample, if the mobile device reports that it is receiving strongersignals from a neighbouring cell such as 100 e than from the source cell100 a, it may be determined that the mobile device should ceasecommunication with the source cell 100 a and commence communication withthe neighbouring cell 100 e. This determination is made by the networkprocessors.

Upon determination that a mobile device 110 a should change the cellwith which it communicates (i.e. upon determination that a ‘handover’should take place), the source cell 100 a operating according to thestandards may send a message known as a Radio Resource Control (RRC)message to the mobile device 110 a. In this case, the message is an “RRCConnection Reconfiguration” message which indicates to the mobile device110 a that its cell connection requires reconfiguration. The messagecontains information sent from the base station 102 f to effecthandover, including an information element known as“MobilityControlInfo”. This information element specifies one targetcell 100 e that the mobile device should attempt to connect to. Usually,the target cell will be the cell from which the mobile device reportedthe strongest signal. However, this is not always the case. For example,the target call may be the cell form which the mobile device reportedthe best quality signal.

In preparing for a handover procedure, the source cell may request oneor more target cells to prepare for the handover by transferring mobiledevice context information to the one or more target cells andinstructing the one or more target cells to reserve resources for themobile device. In return, one or more of the target cells may return apositive response and thus become a “prepared cell”. The source cell mayalso be considered a prepared cell. A prepared cell may therefore be thesource cell 100 a or one or more of the target cells, such as targetcell 100 e.

In attempting to connect to a target cell 100 e, a mobile device 110 aoperating according to the standards will perform the followingprocedures. It will attempt to achieve time synchronization with thesignals emitted by the base station in respect of the target cell; itwill attempt to perform a random access procedure; and, if the foregoingprocesses are successful, it will attempt to start normal downlink (DL)and uplink (UL) data communication with the base station via the targetcell. The UE may attempt to receive system information from the basestation in respect of the target cell before, during, and/or after theseprocedures. Once the mobile device has successfully connected to thetarget cell, that cell becomes the source cell.

Occasionally, a mobile device 110 a may be unable to connect to thetarget cell 100 e. This may be because one of the aforementionedprocedures fails or takes longer than a predetermined length of timedue, possibly to due to poor radio channel conditions, or for otherreasons. In this eventuality, the mobile device 110 a will fail toconnect to the target cell 100 e or in other words, suffer ‘handoverfailure’.

In more detail, handover may fail in a number of scenarios, which amobile device operating according to the standards may encounter, as itattempts a handover procedure. These include the following:

-   -   1. Failing to synchronize with the target cell;    -   2. Failing to receive master information block (MIB) of the        target cell;    -   3. Random access failure (random access itself is a multi-state        procedure which may fail in any step due to poor channel        conditions or erroneous UE/network behaviour);    -   4. Failing to receive system information blocks of the target        cell; and    -   5. Failing to receive/apply target cell dedicated configuration,        including security configuration

According to the standards, handover or connection failure may triggerwhat is known as an “RRC Connection Reestablishment Procedure”. Inaccordance with the standards set in TS36.331, this procedure isinitiated by the mobile device 110 a, and involves the mobile device 110a selecting a cell with which it will attempt to communicate. If thecell selected by the mobile device during the RRC ConnectionReestablishment procedure is a prepared cell and reestablishment ofconnection to the cell is successful, telecommunication proceeds largelyuninterrupted. However, if the cell selected by the mobile device duringthe RRC Connection Reestablishment procedure is a not a prepared cell,the mobile device 110 a will have no knowledge of the communicationparticulars, and the RRC connection of the mobile device will bereleased. This will terminate any extant mobile telecommunications,including telephone calls, data connections, and so on; and will thus beextremely disruptive for the mobile device user.

The following is based on an extract from TS36.304, and describes a cellselection process carried out by a mobile device during areestablishment procedure according to the standards in more detail. Amobile device 110 a-110 c operating according to the standards may carryout cell selection in one of two ways. The first, known as “StoredInformation Cell Selection” uses information on carrier frequencies and,optionally, cell parameters, which has been stored in the mobile device110 a-110 c based on previously received MobilityControlInfo informationelements from a base station 102 a-102 g, or from previously detectedcells 100 a-100 e. Once the mobile device 110 a-110 c has found asuitable cell 100 a-100 e to connect to, it may attempt to connect toit. If no suitable cell 100 a-100 e is found, the mobile device 110a-110 c may carry out the second cell selection procedure, known as“Initial Cell Selection”, which simply involves the mobile device 110a-110 c scanning all available channels in the appropriate frequencybands to find a suitable cell 100 a-100 e. Once a suitable cell 100a-100 e is found, the mobile device 110 a-110 c may attempt to connectto it.

In more detail, a cell selection criterion ‘S’ according to thestandards is fulfilled when the ‘cell selection receiving value’ (dB)S_(rxlev)>0 and the ‘cell selection quality value’ (dB) S_(qual)>0.These quantities are established according to the following explanation,in accordance with the standards set in TS36.101.

Let P_(EmAX) be the maximum transmission power level (in dBm) which agiven mobile device may use when transmitting on the uplinkcommunication channel in the source cell.

Let P_(PowerClass) be the maximum receiving output power (in dBm) of thegiven mobile device according to the mobile device's power class asdefined in TS36.101.

If P_(EMAX) is greater than P_(PowerClass), then let P_(compensation) bethe difference between those values. Otherwise, set P_(compensation) to0. In other words, let P_(compensation) be equal tomax(P_(EMAX)−P_(PowerClass), 0).

Let Q_(rxlevmeas) be the measured cell receiving level value, andQ_(qualmeas) be the measured cell quality level value.

Let Q_(rxlevmin) be the minimum required receiving level value in thecell, and Q_(qualmin) be the minimum required quality level value in thecell.

Let Q_(rxlevminoffset) be the offset to the signalled Q_(rxlevmin) takeninto account in the S_(rxlev) evaluation as a result of a period searchfor a higher priority ‘public land mobile network’(PLMN) whilstoperating in the ‘visited public land mobile network’ (VPLMN), inaccordance with the standards set out in TS36.423. Likewise, letQ_(qualminoffset) be the offset to the signalled Q_(qualmin) taken intoaccount in the S_(qual) evaluation as a result of a period search for ahigher priority PLMN whilst operating in the VPLMN. The signalled valuesQ_(rxlevminoffset) and Q_(qualminoffset) are only applied when a cell isevaluated for cell selection as a result of a periodic search for ahigher priority PLMN while operating in a VPLMN. During the periodicsearch, the mobile device may check the ‘S’ criteria of a cell usingparameter values stored from a different cell of this higher priorityPLMN.

Following on from the above:

S _(rxlev) =Q _(rxlevmeas)−(Q _(rxlevmin) +Q _(rxlevminoffset))−P_(compensation);  1.

and

S _(qual) =Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset))  2.

Confidential studies which are not part of the prior art and which havebeen carried out for the purposes of the present disclosure have shownthat in at least 42.3% of handover failures, there is more than one(i.e. at least two) neighbouring cells which, at the time of handoverfailure, are providing a strong signal (i.e. at within a difference ofat most 6 dB) to the mobile device. This is illustrated by a series ofsimulations shown in FIGS. 1 and 2 and described below.

The first simulation is of a scenario shown in FIG. 5. This scenariowill be referred to as the ‘far’ scenario. FIG. 5 illustrates a plan ofa plurality of cells, including source cell 500. Each cell is served bya base station 502 a-502 c and is bounded by cell borders 504, 506. Eachmobile device 508 is represented by a dot and is served by source cell500. In this scenario, each mobile device is at least one cell radiusaway from the base station of the source cell.

The second simulation is of a scenario shown in FIG. 6. This scenariowill be referred to as the ‘cell border’ scenario. Again, FIG. 6illustrates a plan of a plurality of cells, including source cell 600.Each cell is served by a base station 602 a-602 d and is bounded by cellborders 604, 606. Each mobile device 608 is represented by a dot and isserved by source cell 600. In this scenario, each mobile device islocated along cell borders 606.

The third simulation is a combination of the first and secondsimulations and will be referred to as the ‘cell-edge’ scenario. In thisscenario, each mobile device is located on a cell border or at least onecell radius away from the base station of the source cell.

For all three scenarios, the number of neighbouring cells that arewithin 6 dB of the source cell is collected. As mentioned above, theterm “neighbouring” in this context does not necessarily meanimmediately adjacent, but includes cells which are close enough to thesource cell to transmit signals which are received by the mobile device.

Table 1 below presents the results of the three simulated scenarios. Itshows the percentage of mobile devices for which a given number ‘N’ ofneighbouring cells is within 6 dB of the source cell. For example, inthe ‘cell border’ scenario, 57.7% of mobile devices have a neighbouringcell that is within 6 dB of the source cell.

TABLE 1 Percentage of drops where the UE receives strong signals fromneighbour cells Number of neighbouring cells ‘N’ within Cell Cell 6 dBof the source cell Far borders edge 0 23.40% 0.00% 18.60% 1 33.70%57.70% 37.40% 2 22.40% 23.30% 23.80% 3 12.20% 11.10% 11.70% 4 5.30%4.40% 4.90% 5 1.70% 2.10% 2.20% 6 0.90% 0.80% 0.80% N > 1 42.9% 42.3%44.0%

As apparent from the final line of table 1, in more than 40% ofsituations, there are more than one (i.e. at least two) neighbouringcells that are within 6 dB of the source cell. In other words, in morethan 40% of situations, there is at least one other cell (in addition tothe source cell and the target cell) that a mobile device could use forhandover purposes, in case handover to the target cell fails.

Despite the availability of more than one cell suitable for being atarget cell to which a mobile device could switch in at least 2 out ofevery 5 situations, current standards only specify one single targetcell in the MobilityControlInfo information elements sent by the basestation for initiating the handover procedure.

In some existing telecommunications networks, and referring again toFIG. 1, the source cell 100 a may prepare a target cell 100 e for ahandover procedure, before transmitting the handover instruction. Inthis case, the base station 102 a serving the source cell prepares allthe required information including one or more of the aforementionedcommunication particulars; the security context; radio configurations;and radio access bear attributes. Upon receipt of the information fromthe base station 102 a serving the source cell 100 a, a base station 102e serving the target cell 100 e may assign resources to support themobile device 110 a before the handover command is sent from the sourcecell to the mobile device.

As before, if the mobile device 110 a fails to handover to the targetcell 100 e, the mobile device 110 a may trigger the cell selectionprocess and attempt connection to a cell of its own selection. Theselected cell may not be a prepared cell, in which case all extantmobile telecommunications will be terminated.

According to the standards set out in TS36.331, before the base station102 a serving the source cell 100 a sends a handover instruction to themobile device 110 a, it may prepare one or more target cells 100 b, 100d, 100 e with which the mobile device 110 a may communicate afterhandover. In this case, the base station 102 e serving the target cell100 e, for instance, generates the instruction for the mobile device 110a to perform the handover procedure, and the base station 102 a servingthe source cell 100 a (and in communication with the mobile device)simply forwards the handover instruction to the mobile device 110 awithout altering the values or information content therein (i.e.transparently).

An exemplified MobilityControlInfo information element according to thestandards set out in TS36.331 that provides the target cell informationto the mobile device is as follows.

MobilityControlInfo ::=   SEQUENCE { targetPhysCellId PhysCellId,carrierFreq CarrierFreqEUTRA OPTIONAL,-- Cond HO-toEUTRAcarrierBandwidth CarrierBandwidthEUTRA OPTIONAL,-- Cond HO-toEUTRAadditionalSpectrumEmission AdditionalSpectrumEmission OPTIONAL,-- CondHO-toEUTRA t304 ENUMERATED { ms50, ms100, ms150, ms200, ms500, ms1000,ms2000, spare1}, newUE-Identity C-RNTI, radioResourceConfigCommonRadioResourceConfigCommon, rach-ConfigDedicated RACH-ConfigDedicatedOPTIONAL, -- Need OP ... }

It will be apparent from the above element that the source base stationmay prepare communication particulars for more than one target cell.Nevertheless, even in this case the MobilityControlInfo informationelement will only ever specify one target cell to the mobile device. Thecommunication particulars include bandwidth, ‘cell radio networktemporary identifier’ (C-RNTI) and ‘random access channel’ (RACH)configuration.

In other systems, it is known that list of target base stationidentifiers (IDs) and a service level prediction of the target basestations is provided to the mobile device in a handover message. Howeverin certain networks, the mobile device is required to have a target cellidentifier (ID) and other essential information including targetfrequency and random access parameters, in order to perform a handover.

The following disclosure relates to an improved handover procedure whichis not part of the prior art.

In one aspect, there is provided a method in a network component for usein a cellular network. The network has a plurality of cells. The methodcomprises transmitting handover information from the network componentto the mobile device. The handover information comprises informationincluding information of a plurality of target cells with which themobile device may subsequently communicate. The handover information mayinclude other information. The network component may be part of a basestation, such as a source base station.

The mobile device may be connected to a source cell when receiving thehandover information transmitted from the network component, and may beunconnected to any one of the plurality of target cells which aredifferent to the source cell, or any other cell.

The network component may be in wireless communication with the mobiledevice prior to the transmission of handover information of theplurality of target cells. Alternatively, the network component may bein communication with another network component, which itself is inwireless communication with the mobile device prior to transmission.

Prior to the step of transmitting handover information, the method maycomprise the optional step of receiving at the network component atleast one communication parameter of the existing communication with themobile device; for instance, communication with the source cell. Thecommunication parameter may be one or more of signal strength and signalquality of the signal received from the network component.

Prior to the step of transmitting handover information, the method maycomprise the optional step of receiving at the network component atleast one communication parameter of at least one candidate target cell,or at least one other cell, transmitted from the mobile device anddetermining, by the network component, based on the at least onecommunication parameter, whether to transmit the handover information.The handover information is only transmitted if said determination ispositive.

The method may further comprise the optional step of initiating aresource allocation procedure of the plurality of target cells. Theresource allocation procedure may comprise one of two steps, namely:communicating directly with one or more network components of theplurality of target cells to reserve resources of said one or morenetwork components of the plurality of target cells for the mobiledevice; or communicating with one or more network components of theplurality of target cells via a control network component to reserveresources of said one or more network components of the plurality oftarget cells for the mobile device.

After the mobile device has initiated communication with a networkcomponent via one of the plurality of target cells, the method maycomprise the optional step of instructing release of resources of eachof the one or more network components of the plurality target cellsother than the network component with which the mobile device is incommunication. The release instruction may come from a source basestation or a target base station with which the mobile device hasinitiated communication. Alternatively, the resources may be releasedonce a predetermined period of time has elapsed.

In a further aspect, there is provided a method in a mobile device foruse in a cellular network. The mobile device may communicate wirelesslywith a plurality of network components in a cellular network having aplurality of cells. The method comprises receiving handover informationat the mobile device from a source cell of the cellular network (i.e.from a source network component of the plurality of network components),wherein the handover information comprises information includinginformation of a plurality of target cells with which the mobile devicemay subsequently communicate. The handover information may include otherinformation. The mobile device may be a mobile telephone such as a‘smart-phone’; a portable laptop computer; a tablet computer or anyother mobile device adapted to communicate using a cellular network.

Immediately prior to the mobile device receiving the handovercommunication it may be in communication with a network component viathe source cell. For instance, the mobile device may be connected to thesource cell when receiving the handover information and may beunconnected to any one of the plurality of target cells which aredifferent to the source cell, or to any other cell. The method may thuscomprise the mobile device, after receiving the handover information:ceasing communication with said network component via said source cell;and attempting to connect to a network component via a first targetcell, the first target cell being one of the plurality of target cells.Upon or after connecting with said network component, the mobile devicemay begin communicating with said network component via said firsttarget cell.

Optionally, the mobile device determines which one of the plurality oftarget cells is to be the first target cell. However, this could be doneinstead by the source base station. The mobile device may determine apriority order for attempting connection to a network component via theplurality of target cells.

The mobile device may attempt to connect to a network component via thefirst target cell, the first target cell being one of the plurality oftarget cells, and upon or after a failure to connect to the networkcomponent via the first target cell, the mobile device may attempt toconnect to a network component via a second target cell, the secondtarget cell being the next target cell after the first target cellspecified according to the priority order.

A failure to connect may be defined by one or more of the followingevents detectable by the mobile device: a communication synchronizationfailure of the mobile device with a network component via the firsttarget cell; a failure of the mobile device to receive a masterinformation block (MIB) of a network component via the first targetcell; a failure of the mobile device to receive a system informationblock (SIB) of a network component via the first target cell; a randomaccess failure in connecting to a network component via the first targetcell; a failure to apply a given configuration required by a networkcomponent via the first target cell, such as a security configuration.

Prior to the step of receiving handover information, the mobile devicemay determine at least one communication parameter of existingcommunication with a network component via the source cell and transmitsaid at least one communication parameter of the existing communicationfrom the mobile device to the network component.

Prior to the step of receiving handover information, the mobile devicemay determine at least one communication parameter of at least onecandidate target cell or other cell; and transmit said at least onecommunication parameter of said at least one candidate target cell orother cell from the mobile device to the network component. Thecommunication parameter may be one or more of signal strength and signalquality of the signal received from the network component.

After handover failure, the mobile device may attempt to perform areestablishment procedure comprising attempting to connect to a networkcomponent via one of the plurality of target cells. For example, themobile device may perform a reestablishment procedure comprisingattempting to connect to a network component via the first target cell,being one of the plurality of target cells, and upon failure to connectto the network component via the first target cell, the mobile devicemay attempt to connect to a network component via a second target cell,being the next target cell after the first target cell specifiedaccording to the priority order.

Optionally, the handover information defines a priority order of thetarget cells.

Optionally, the handover information comprises: a target frequency valueor range for communicating with a network component via each targetcell; and access parameters for a network component communicable viaeach target cell. The handover information may comprise communicationparameters of each target cell sufficient for the mobile device toinitiate communication with a network component via each target cellwithout requiring prior coordination of each target cell forcommunicating with the mobile device. Preferably, the handoverinformation is sufficient to enable the mobile device to perform ahandover operation to a target cell. Therefore, the device does notrequire additional information to perform the handover.

The handover information may comprise cell identification informationfor one or more target cells.

The handover information may comprise communication parameters of afirst target cell sufficient for the mobile device to attempt toinitiate communication with the first target cell without requiringprior coordination of the first target cell and/or target cells forcommunicating with the mobile device, and further comprises cellidentification information for each subsequent target cell. The handoverinformation may comprise only cell identification information for eachsubsequent target cell. In this case, the source cell could coordinateeach of the subsequent target cells for communication with the mobiledevice, such as by making the communication particulars the same asthose of the source cell.

The handover information may comprise communication parameters of atleast one target cell sufficient for the mobile device to initiatecommunication with a network component via the at least one target cellwithout requiring prior coordination of the at least one target celland/or other target cells for communicating with the mobile device,wherein the handover information further comprises communicationparameters of additional target cells comprising or consisting only ofdifferences between required communication parameters of the additionaltarget cells and the previously-transmitted communication parameters ofthe at least one target cell.

The handover information may be transmitted in a radio resource control(RRC) connection reconfiguration message transmitted to the mobiledevice.

In a further aspect, there is provided a network component for use in acellular network, the network having a plurality of cells. The networkcomponent comprises: a processing unit configured to generate handoverinformation; and a transmitter configured to transmit the handoverinformation to a mobile device, wherein the handover informationcomprises information including information of a plurality of targetcells with which the mobile device may subsequently communicate.

The processing unit may be further adapted to receive from the mobiledevice at least one communication parameter of the existingcommunication with the mobile device.

The processing unit may be further configured to receive at least onecommunication parameter of at least one candidate target celltransmitted from the mobile device; determine, based on the at least onecommunication parameter, whether to transmit the handover information;and transmit the handover information if said determination is positive.

Optionally, the processing unit may be further configured to initiate aresource allocation procedure of the plurality of target cells. To thatend, the processing unit may be configured to communicate directly withnetwork components of the plurality of target cells and reserveresources of the network components of the plurality of target cells forthe mobile device; or communicate with the network components of theplurality of target cells via a control network component and reserveresources of the network components of the plurality of target cells forthe mobile device.

The processing unit may be further configured to instruct release ofresources of each of the network components of the plurality targetcells other than the network component with which the mobile device isin communication. Alternatively, the resources may be released by anetwork component of a target cell, or once a predetermined period oftime has elapsed.

In a further aspect, there is provided a mobile device for communicatingin a cellular network. The mobile device may communicate wirelessly withthe network, which may have a plurality of cells. The mobile devicecomprises: a receiver configured to receive handover information (e.g.from a network component); and a processing unit adapted to process thehandover information, wherein the handover information comprisesinformation including information of a plurality of target cells withinwhich the mobile device can subsequently communicate.

The processing unit may be further configured to cease communicationwith a network component via a source cell upon receipt of the handovercommunication; and initiate communication with a network component viaone of the plurality of target cells.

The processing unit may be further configured to connect to a networkcomponent via a first target cell, the first cell being one of theplurality of target cells, and communicate with said network componentvia said first target cell.

The processing unit may be further configured to determine which one ofthe plurality of target cells is to be the first target cell. However,this could be done instead by the source base station. For example, themobile device may be further configured to determine a priority orderfor attempting connection to a network component via the plurality oftarget cells.

The processing unit may be further configured to attempt to connect to anetwork component via the first target cell, being one of the pluralityof target cells, and upon failing to connect to the network componentvia the first target cell, attempt to connect to a network component viaa second target cell, being the next target cell after the first targetcell specified according to the priority order.

The processing unit may be further configured to connect to a networkcomponent via the second target cell, being one of the plurality oftarget cells, and communicate with said network component via saidsecond target cell.

The processing unit may be further configured to determine at least onecommunication parameter of existing communication with a networkcomponent via the source cell; and transmitting said at least onecommunication parameter of the existing communication to the networkcomponent.

The processing unit may be further configured to determine at least onecommunication parameter of at least one candidate target cell; andtransmit said at least one communication parameter of said at least onecandidate target cell to the network component.

The processing unit may be further configured to perform areestablishment procedure comprising attempting to connect to a networkcomponent via one of the plurality of target cells.

The processing unit may be further configured to perform areestablishment procedure comprising attempting to connect to a networkcomponent via the first target cell, being one of the plurality oftarget cells, and on failing to connect to the network component via thefirst target cell, attempting to connect to a network component via asecond target cell, being the next target cell after the first targetcell specified according to the priority order.

In a further aspect there is provided a computer readable medium havingcomputer readable instructions stored thereon, the instructionsexecutable by a processor to cause the processor to generate handoverinformation for use in a handover procedure of a mobile device operatingwithin a cellular network, the handover information comprisinginformation including information of a plurality of target cells withwhich the mobile device may subsequently communicate.

In a further aspect there is provided a computer readable medium havingcomputer readable instructions stored thereon, the instructions adapted,when executed by a processor, to cause the processor to process handoverinformation for use in a handover procedure of a mobile device operatingwithin a cellular-based communications network having a plurality ofcells, the handover information comprising information of a plurality oftarget cells within which the mobile device can subsequentlycommunicate.

In a further aspect there is provided a method in a mobile device foruse in a cellular network. The method comprises commencing a radioresource control (RRC) connection reestablishment procedure, theprocedure comprising performing a cell selection operation wherein oneor more target cells which the mobile device may select forre-establishment are specified in handover information previouslyreceived at the mobile device. However, it will be appreciated that thecell or cells which the mobile device may select for re-establishmentneed not be limited to those specified in the handover information, andmay be known to the mobile device or detected as described above.

Prior to the step of commencing a radio resource control (RRC)connection reestablishment procedure, the method may further comprisereceiving the handover information at the mobile device, and preferablyattempting to connect to a first target cell. The mobile device may failto connect to the first target cell or in other words may experience‘handover failure’. the step of commencing a radio resource control(RRC) connection reestablishment procedure occurs upon or after handoverfailure. The first target cell may be a target cell specified in thehandover information.

The handover information may comprise information of a plurality oftarget cells with which the mobile device may subsequently communicate.Prior to the step of commencing a radio resource control (RRC)connection reestablishment procedure, the method may further comprisethe mobile device attempting to connect to a first target cell, beingone of the plurality of target cells.

The handover information may be received in a radio resource control(RRC) connection reconfiguration message transmitted to the mobiledevice.

The method may further comprise the mobile device selecting a cell forreestablishment. The cell selected for reestablishment may be one of aplurality of cells, including one or more target cells specified in thehandover information and one or more cells not specified in the handoverinformation. The cells not specified in the handover information may becells which are known to the mobile device, or cells which the mobiledevice detects.

The mobile device may determine which one of the plurality of cells isto be the first cell it selects for reestablishment. The mobile devicemay determine a priority order for the plurality of target cells to beselected for reestablishment. Thus, should the mobile device fail toconnect to the first cell (i.e. fail to complete reestablishment withthe first cell), the mobile device may attempt to connect to a secondcell, being the next cell after the first cell specified according tothe priority order.

The mobile device may prioritise selecting one kind of cell over anotherkind. For example, the mobile device may prioritise selecting or moretarget cells specified in the handover information over other cells(i.e. cells not specified in the handover information, such as cellswhich are known to the mobile device, or cells which the mobile devicedetects).

The method may comprise determining, by the mobile device, at least onesignal parameter of one or more target cells specified in the handoverinformation. The signal parameter may include one or more of signalquality and signal strength. The mobile device may select a cell forreestablishment based on the at least one signal parameter. For example,the cell selected for reestablishment may be a target cell specified inthe handover information if the at least one signal parameter of the oneor more target cells specified in the handover information is greaterthan a predetermined threshold. The predetermined threshold may be fixedor variable, and may be set by the mobile device, source cell or one ormore target cells.

The method may comprise determining, by the mobile device, at least onesignal parameter of a cell not specified in the handover information;and comparing the at least one signal parameter with at least one signalparameter of one or more target cells specified in the handoverinformation. The mobile device may select a cell for reestablishmentbased on the comparison between the sets of at least one signalparameter. For example, the cell selected for reestablishment may be atarget cell specified in the handover information if: the differencebetween a) the at least one signal parameter of the one or more targetcells specified in the handover information, and b) the at least onesignal parameter of the cell not specified in the handover information,is less than a predetermined threshold. Again, the predeterminedthreshold may be fixed or variable, and may be set by the mobile device,source cell or one or more target cells.

In a situation where more than one cell satisfies the condition requiredby the predetermined threshold, the cell selected for reestablishmentmay be the target cell specified in the handover information having theat least one signal parameter which is closest to the at least onesignal parameter of the cell not specified in the handover information.

The cell selected for reestablishment may be the cell not specified inthe handover information if: the difference between a) the at least onesignal parameter of the one or more target cells specified in thehandover information, and b) the at least one signal parameter of thecell not specified in the handover information, is greater than apredetermined threshold. Again, the predetermined threshold may be fixedor variable, and may be set by the mobile device, source cell or one ormore target cells.

As discussed above with respect to the contents of the handoverinformation, the handover information may comprise cell identificationinformation for the one or more each target cell. The handoverinformation may comprise only cell identification information for theone or more each target cell.

In a further aspect there is provided a method in a network componentfor use in a cellular network. The method comprises transmittinghandover information for use in a reestablishment procedure from thenetwork component to a mobile device; wherein the handover informationcomprises information of a target cell with which the mobile device maysubsequently communicate.

The information handover comprises information of a plurality of targetcells with which the mobile device may subsequently communicate. Thehandover information is transmitted in a radio resource control (RRC)connection reconfiguration message.

For at least one target cell specified in the handover information, thehandover information may further specify a predetermined thresholdindicating the minimum permissible level of signal parameter of the saidat least one target cell specified in the handover information. Thepredetermined threshold may be fixed or variable. The at least onesignal parameter may include one or more of signal quality and signalstrength. The minimum permissible level prevents target cells not havingthe requisite parameter (for instance, having poor signal strength orpoor signal quality) from being selected by the mobile device.

For at least one target cell specified in the handover information, thehandover information may further specify a predetermined thresholdindicating the maximum permissible difference between at least onesignal parameter of the said at least one target cell specified in thehandover information and at least one signal parameter of a cell notspecified in the handover information. The predetermined threshold maybe fixed or variable. The maximum permissible difference prevents targetcells having a parameter which is too far from another (such as signalstrength or signal quality too much lower than a detected cell, forexample) from being selected.

The handover information may further specify that if the differencebetween a) the at least one signal parameter of the said at least onetarget cell specified in the handover information, and b) the at leastone signal parameter of the cell not specified in the handoverinformation, is less than a predetermined threshold, the mobile deviceshould select the said at least one target cell specified in thehandover information. Alternatively, the handover information mayfurther specifies that if the difference between a) the at least onesignal parameter of the said at least one target cell specified in thehandover information, and b) the at least one signal parameter of thecell not specified in the handover information, is more than apredetermined threshold, the mobile device should select the cell notspecified in the handover information.

As discussed above with respect to the contents of the handoverinformation, the handover information may comprise cell identificationinformation for the one or more each target cell. The handoverinformation may comprise only cell identification information for theone or more each target cell.

In a further aspect, there is provided a mobile device for communicatingin a cellular network. The mobile device comprises a receiver configuredto receive handover information from one of a plurality of cells; and aprocessing unit adapted to process the handover information; wherein theprocessor is adapted to commence a radio resource control (RRC)connection reestablishment procedure and perform a cell selectionoperation wherein one or more target cells which the mobile device mayselect for re-establishment are specified in handover informationpreviously received at the mobile device.

In a further aspect, there is provided a network component for use in acellular network, the network having a plurality of cells, the networkcomponent comprising: a processing unit configured to generate handoverinformation for use in a radio resource control (RRC) connectionreestablishment procedure; a transmitter configured to transmit thehandover information to a mobile device, wherein the handoverinformation comprises information of a target cell with which the mobiledevice may subsequently communicate.

In a further aspect, there is provided a computer readable medium havingcomputer readable instructions stored thereon, the instructionsexecutable by a processor to cause the processor to process handoverinformation for use in a radio resource control (RRC) connectionreestablishment procedure of a mobile device operating within a cellularnetwork.

In a further aspect, there is provided a computer readable medium havingcomputer readable instructions stored thereon, the instructionsexecutable by a processor to cause the processor to generate handoverinformation for use in a radio resource control (RRC) connectionreestablishment procedure of a mobile device operating within a cellularnetwork.

The devices and methods described henceforth relate to a source basestation which provides additional information to a mobile device toenable the mobile device to attempt to connect to one or more ‘further’target base stations in addition to the first target base station so asto reduce the incidences of terminating mobile telecommunications in theevent of handover failure.

The devices and methods described henceforth are particularlyadvantageous because the aforementioned studies have shown that it isoften the case that a mobile device can receive suitably strong signalsto support mobile telecommunication from more than one cell; yetfollowing conventional communication standards, none of the strong cellsmay be a prepared cell. The devices and methods described henceforthpermit information of more than one target or prepared cell to be sentto the mobile device, optionally in a priority order. This facilitatesthe mobile device in connecting to a target cell without terminatingmobile communication.

Moreover, it will be appreciated that when the target and source cellshave weak signals, the mobile device has no option but to attempt toestablish connection to one of the cells and then wait for the networkto signal a new target cell according to measurement results. Normaldownlink and uplink operations may require retransmission of data, ortrigger transmission failure in such cases. Furthermore, the optionalprocesses of performing measurements, triggering reports, negotiating anew target cell, and finally signalling the new target cell to themobile device are time-consuming. During this time the mobile device maygo out of coverage. The devices and methods described henceforth permitthe mobile device to attempt a handover to a better target cell, therebyreducing call interruption times and delay.

The devices and methods described henceforth reduce the number ofhandover negotiations and handover failures in the network and hencereduce network communication loads.

The devices and methods described henceforth may be applicable to anyradio access technology where some form of mobility is supported. Assuch, they might be applicable, but not limited, to: ‘Evolved UniversalTerrestrial Radio Access’ (E-UTRA) ‘Long Term Evolution’ (LTE);‘Universal Mobile Telecommunications System’ (UMTS); and ‘CodeDivisional Multiple Access’ (CDMA) at least. However, the detailedexemplary description below concerns radio access technology in the formof LTE/E-UTRA (Release 8 and Release 9) for conciseness.

An example of a cellular network 9000 is shown in FIG. 9. Here fivecells 900 a-900 e are shown, each served by at least one base-station902 a-902 g. One of the cells, 900 c, illustrated is served by two basestations 902 c, 902 g. Moreover, one of the base stations, 902 f,illustrated serves three cells 902 a, 902 b and 902 d. The skilledperson will appreciate that the illustrated cellular network is anexample which illustrates the principle, and more complex arrangementsof cells and base stations are possible. With the exception of thefollowing description, cellular network 9000 comprises correspondingcomponents to cellular network 1000 described with reference to FIG. 1.The same is true of base station 200 of FIG. 2, mobile device 300 ofFIG. 3 and mobile management entity 400 of FIG. 4.

At least one of the mobile devices 910 a-910 c, base-stations 902 a-902g, cells 900 a-900 e, mobile management entity 904 a, 904 b andcorresponding methods described henceforth are adapted to utilise aMobilityControlInfo information element which specifies more than onetarget cell. For example, whilst a base station serving a source cellmay specify only one target cell to a mobile device with which it is incommunication, it may also be adapted to specify more than one (i.e. twoor more) target cells. Likewise, a mobile device may be adapted toattempt handover with more than one target cell and/or initiate thereestablishment procedure with more than one target cell.

For example, with reference to FIG. 9, when the source base station 902a prepares multiple target cells, such as 900 b, 900 d and 900 e, a listof the prepared cells 900 b, 900 d and 900 e may be indicated ascandidate target cells. The mobile device 910 a may apply the existinghandover procedure for each target cell 900 b, 900 d and 900 e inaccordance with standards set out in TS36.331. If the mobile device 910a fails all or some of the target cells 900 b, 900 d and 900 e provided,the mobile device 910 a may perform a reestablishment procedure asdescribed above and in accordance with the current standards set out inTS36.331. Optionally, the source base station 902 a may indicate whetherinformation on one or multiple target cells 900 b, 900 d and 900 e willbe provided. For example, the source base station may include multipletarget cells 900 b, 900 d and 900 e when the source base station 902 ahas radio link failure reports more than a given threshold.Alternatively, when a time critical service is being received by themobile device 910 a or sufficient network resources are not available,the source base station 902 a may limit the number of target cells toone or a small number such as one, two, three, four or more, or thesource base station 902 a may set the mobile device 910 a a shorterperiod of time for the mobile device 910 a to complete a handoverattempt to each of the multiple target cells 900 b, 900 d and 900 e.

A first exemplary method according to foregoing description isillustrated in FIG. 7 which illustrates the messages which may be sentbetween a mobile device 700, a source base station 702 serving a sourcecell; a first target base station 704 serving a first target cell; and asecond target base station 706 serving a second target cell.

The mobile device 700 may be initially wirelessly connected forcommunications to the base station 702 serving the source cell. As isconventional, the mobile device 700 may perform measurements of thestrength of any signals received from the source cell and neighbouringcells and periodically send a report (708 a-708 c) to the source cellfor processing.

The base station 702 serving the source cell, or a processor coupled tothat base station 702, may analyse the report and may then evaluatewhether the mobile device 700 should continue to be served by the sourcecell, or whether it would be better served by a neighbouring cell. Onceit is determined that the mobile device might be better served by aneighbouring cell, the source cell may prepare an RRC ConnectionReconfiguration message that indicates to the mobile device 700 that itscell connection requires reconfiguration. This message may containinformation sent from the source base station 702 to effect handover,including an information element known as MobilityControlInfo.

In the example shown in FIG. 7, the MobilityControlInfo sent by thesource base station 702 may contains instructions for the mobile device700 to:

-   1) attempt a handover procedure to cease its connection to the    source base station 702 serving the source cell and establish a    connection with the first target cell;    -   and, if handover fails (for example, is not complete after        expiry of the T304 timer):-   2) attempt a handover procedure to cease its connection to the    source base station 702 serving the source cell and establish a    connection with the second target cell.

Whilst only two target base stations and corresponding target cells areillustrated in this embodiment, it will be appreciated that any numberof target base stations and target cells may be employed, and theMobilityControlInfo may accordingly contain instructions for the mobiledevice 700 to attempt connection to any number of target base stationsserving any number of target cells following handover failure. In thatregard, it will be appreciated that a target base station may serve morethan one target cell, and a target cell may be serviced by more than onetarget base station.

In the example shown in FIG. 7, the MobilityControlInfo specifies a listof target cells, each entry may contain the complete communicationparticulars of each target cell suitable for the mobile device 700 toconnect to the base station serving that cell, including the bandwidth,C-RNTI and RACH configuration. Since complete information for eachtarget cell is provided to the mobile device, the embodiment of FIG. 7may be particularly flexible for inter-frequency handover cases.

In the illustrated example, the list of target cells is in the priorityorder in which the mobile device is to attempt to handover to them.However, the list could be in a different order, or no order at all.Moreover, it could be left to the mobile device to select the order inwhich handover is attempted.

An example specification of the MobilityControlInfo suitable for puttingthe embodiment shown in FIG. 7 into effect is given below. The textbetween the symbol ‘***’ is a change with respect to the current RRCspecification given in TS36.331.

*** MobilityControlInfo ::=     SEQUENCE {     targetCellInfoList    SEQUENCE (SIZE (1..maxCells)) OF TargetCellInfo, } ***targetCellInfo ::=     SEQUENCE { targetPhysCellId PhysCellId,carrierFreq CarrierFreqEUTRA OPTIONAL,-- Cond HO-toEUTRAcarrierBandwidth CarrierBandwidthEUTRA OPTIONAL,-- Cond HO-toEUTRAadditionalSpectrumEmission AdditionalSpectrumEmission OPTIONAL,-- CondHO-toEUTRA t304 ENUMERATED { ms50, ms100, ms150, ms200, ms500, ms1000,ms2000, spare1}, newUE-Identity C-RNTI, radioResourceConfigCommonRadioResourceConfigCommon, rach-ConfigDedicated RACH-ConfigDedicatedOPTIONAL, -- Need OP ... }

Flow charts illustrating the first exemplary method are shown in FIGS.11A and 11B.

As shown in FIG. 11A, the source base station receives 1100 a reportfrom a mobile device indicating communication parameters such as signalstrength and signal quality in respect of one or more of the sourcecell, and one or more of the neighbouring cells. This step is optional,however. If certain conditions (described above) are met, the sourcebase-station will determine 1102 that the mobile device should becommunicating with a different cell (i.e. determine that a handover isrequired) and will prepare 1104 a list of target cells to which themobile device may handover. The source base station will transmit 1106 ahandover message (described above) containing the complete communicationparticulars of each target cell suitable for the mobile device toconnect to the target base station.

As shown in FIG. 11B, the mobile device transmits 1108 to the sourcebase station a report indicating communication parameters such as signalstrength and signal quality in respect of one or more of the sourcecell, and one or more of the neighbouring cells. This step is optional,however. At some point, the mobile device will receive 1110 a handovermessage from the source base station. As described above, the handovermessage contains the complete communication particulars of each targetcell suitable for the mobile device to connect to a target base station.The mobile device will then cease communication 1112 with the sourcecell and attempt to handover 1114 to the first target cell in theplurality of target cells in the handover message. If handover issuccessful 1116, the mobile device will commence communication 1118 withthe first target cell. If handover is unsuccessful 1116, the mobiledevice will attempt to handover 1120 to the second target cell in theplurality of target cells in the handover message. If handover issuccessful 1122, the mobile device will commence communication 1124 withthe second target cell. If handover is unsuccessful 1122, the processmay be repeated for each of the plurality of target cells in thehandover message. If handover is unsuccessful for each of the pluralityof target cells in the handover message, the mobile device may initiatea reestablishment procedure 1126, as described above.

A second exemplary method differs from the first method illustrated inFIGS. 3 and 11A and B in the following respects.

Instead of providing the mobile device with the complete communicationparticulars of each of the target cells listed in theMobilityControlInfo, the complete communication particulars of the firsttarget cell listed in the MobilityControlInfo may be provided, and onlythe physical cell identity of the further target cells may be provided.It will be appreciated that when only the physical cell identity of eachof the plurality of further target cells is provided in theMobilityControlInfo element of the RRC Connection Reconfigurationmessage, the size of the message is reduced as compared with the messagerequired in the method above.

The second exemplary method is possible because in some instances, allcells belonging to a given network will have the same bandwidth.Moreover, certain mobile devices may be capable of detecting thebandwidth of a given target cell. Accordingly, it is not alwaysnecessary to provide the mobile device with the bandwidth information.Furthermore, as will be described below with reference to FIG. 4, it ispossible to configure base stations of a cellular network in such a wayas to remove the need to inform a mobile device of all communicationparticulars for the target cells by coordinating all the target cells touse the same resources.

An example specification of the MobilityControlInfo suitable for puttingthe second exemplary method into effect is given below. Again, the textbetween the symbol ‘***’ is a change with respect to the current RRCspecification given in TS36.331, and the text in ‘[‘/’]’ is text that isremoved.

MobilityControlInfo ::=     SEQUENCE { [[[targetPhysCellIdPhysCellId,]]] *** targetPhysCellIdList     SEQUENCE (SIZE(1..maxCells)) OF PhysCellId, *** carrierFreq CarrierFreqEUTRAOPTIONAL,-- Cond HO-toEUTRA carrierBandwidth CarrierBandwidthEUTRAOPTIONAL,-- Cond HO-toEUTRA additionalSpectrumEmissionAdditionalSpectrumEmission OPTIONAL,-- Cond HO-toEUTRA t304 ENUMERATED {ms50, ms100, ms150, ms200, ms500, ms1000, ms2000, spare1},newUE-Identity C-RNTI, radioResourceConfigCommonRadioResourceConfigCommon, rach-ConfigDedicated RACH-ConfigDedicated OPTIONAL, -- Need OP ... }

Flow charts illustrating the second exemplary method are shown in FIGS.12A and 12B. As can be seen, the flow charts of FIGS. 12A and 12B arethe same as those in 11A and 11B, except for the content of the handovermessage, which provides only the physical identity of the target cells.

According, the source base station receives 1200 a report from a mobiledevice indicating communication parameters such as signal strength andsignal quality in respect of one or more of the source cell, and one ormore of the neighbouring cells. This step is optional, however. Ifcertain conditions (described above) are met, the source base-stationwill determine 1202 that the mobile device should be communicating witha different cell (i.e. determine that a handover is required) and willprepare 1204 a list of target cells to which the mobile device mayhandover. The source base station will transmit 1206 a handover message(described above) containing the complete communication particulars ofthe first target cell and only the physical identity of each furthertarget cell.

As shown in FIG. 12B, the mobile device transmits 1208 to the sourcebase station a report indicating communication parameters such as signalstrength and signal quality in respect of one or more of the sourcecell, and one or more of the neighbouring cells. This step is optional,however. At some point, the mobile device will receive 1210 a handovermessage from the source base station. As described above, the handovermessage contains the complete communication particulars of the firsttarget cell and only the physical identity of the plurality of furthertarget cells which the mobile device may attempt to connect to. Themobile device will then cease communication 1212 with the source celland attempt to handover 1214 to the first target cell in the pluralityof target cells in the handover message. If handover is successful 1216,the mobile device will commence communication 1218 with the first targetcell. If handover is unsuccessful 1216, the mobile device will attemptto handover 1220 to the second target cell in the plurality of targetcells in the handover message. If handover is successful 1222, themobile device will commence communication 1224 with the second targetcell. If handover is unsuccessful 1222, the process may be repeated foreach of the plurality of target cells in the handover message. Ifhandover is unsuccessful for each of the plurality of target cells inthe handover message, the mobile device may initiate a reestablishmentprocedure 1226, as described above.

A third exemplary method differs from the first and second methodsillustrated in FIG. 3 and described above in the following respects.

Instead of providing the mobile device with the complete communicationparticulars of each of the target cells (as with the first method) andinstead of omitting the communication particulars and providing themobile device with only the physical cell identity (as with the secondmethod), the third method provides an alternative approach.

In this third method, the communication particulars of target cells areprepared by the base stations serving the target cells themselves andare then sent to the source cell. The plurality of target cells listedin the MobilityControlInfo element of the RRC Connection Reconfigurationmessage sent by the source cell to the mobile device may be specifiednot in terms of their complete communication particulars, or solely bytheir physical cell identity, but in terms of differences (i.e. deltas)with the particulars of the source cell. As with the second method, thecomplete communication particulars of the first target cell areprovided.

The differences with the given target cell may include only the physicalcell identity or may include all fields of the complete configuration ofthe MobilityControlInfo element, depending how different the targetcells are.

An example specification of the MobilityControlInfo suitable for puttingthe third method into effect is given below. Again, the text between thesymbol ‘***’ is an addition with respect to the current RRCspecification given in TS36.331, and the text in ‘[[‘/’]]’ is text thatis removed.

*** MobilityControlInfo ::=     SEQUENCE {     FirstTargetCellInfotargetCellInfo,     AdditionalTargetCellsInfo     SEQUENCE (SIZE(1..maxCells−1)) OF targetCellInfo, OPTIONAL - Need ON } ***targetCellInfo ::=     SEQUENCE { targetPhysCellId PhysCellId,carrierFreq CarrierFreqEUTRA OPTIONAL, -- ***Need OP*** [[CondHO-toEUTRA]] carrierBandwidth CarrierBandwidthEUTRA OPTIONAL, -- ***NeedOP*** [[Cond HO-toEUTRA]] additionalSpectrumEmissionAdditionalSpectrumEmission OPTIONAL, -- ***Need OP*** [[CondHO-toEUTRA]] t304 ENUMERATED { ms50, ms100, ms150, ms200, ms500, ms1000,ms2000, spare1}, newUE-Identity C-RNTI, OPTIONAL,    -- Need ONradioResourceConfigCommon RadioResourceConfigCommon, OPTIONAL, -- Need***OP*** [[ON]] rach-ConfigDedicated RACH-ConfigDedicated  OPTIONAL, --Need ***ON*** [[OP]] ... }

Flow charts illustrating the third exemplary method are shown in FIGS.13A and 13B. As can be seen, the flow charts of FIGS. 13A and 13B arethe same as those in 12A and 12B, except for the content of the handovermessage, which provides only the differences between the communicationparticulars of the targets cells from the source cell.

Accordingly, the source base station receives 1300 a report from amobile device indicating communication parameters such as signalstrength and signal quality in respect of one or more of the sourcecell, and one or more of the neighbouring cells. This step is optional,however. If certain conditions (described above) are met, the sourcebase-station will determine 1302 that the mobile device should becommunicating with a different cell (i.e. determine that a handover isrequired) and will prepare 1304 a list of target cells to which themobile device may handover. The source base station will transmit 1306 ahandover message (described above) containing the complete communicationparticulars of the first target cell and the differences between thecommunication particulars of the further targets cells and the firsttarget cell.

As shown in FIG. 13B, the mobile device transmits 1308 to the sourcebase station a report indicating communication parameters such as signalstrength and signal quality in respect of one or more of the sourcecell, and one or more of the neighbouring cells. This step is optional,however. At some point, the mobile device will receive 1310 a handovermessage from the source base station. As described above, the handovermessage contains the complete communication particulars of the firsttarget cell and the differences between the communication particulars ofthe further target cells with which the mobile device may handover andthe first target cell. The mobile device will then cease communication1312 with the source cell and attempt to handover 1314 to the firsttarget cell in the plurality of target cells in the handover message. Ifhandover is successful 1316, the mobile device will commencecommunication 1318 with the first target cell. If handover isunsuccessful 1316, the mobile device will attempt to handover 1320 tothe second target cell in the plurality of target cells in the handovermessage. If handover is successful 1322, the mobile device will commencecommunication 1324 with the second target cell. If handover isunsuccessful 1322, the process may be repeated for each of the pluralityof target cells in the handover message. If handover is unsuccessful foreach of the plurality of target cells in the handover message, themobile device may initiate a reestablishment procedure 1326, asdescribed above.

As mentioned above, it is possible to configure base stations of acellular network to remove the requirement for the source base stationto transmit some or all of the communication particulars for the targetcells to the mobile device. In summary, this process involves the sourcebase station negotiating the same communication particulars such asC-RNTI and RACH configuration for the target cells as the source cell,or for further target cells as the first cell. This procedure may beimplemented with any of the first to third methods described above. Thisprocedure is explained in more detail below, with reference to FIG. 4which illustrates the messages that may be sent between a source basestation 400 serving a source cell; a first target base station 402serving a first target cell; and a second target base station 406serving a second target cell, optionally via a mobility managemententity (MME) 404. The source base station is configured to negotiatewith one or more target base stations either through a directconnection, such as an ‘X2 link’ or through an indirect connection, suchas an ‘S1 interface’ with the MME. In the example shown in the figures,the base station 400 serving the source cell communicates with the basestation 402 serving the first target cell directly, such as over an X2link; whilst it communicates with the base station 406 serving thesecond target cell indirectly, such as via an S1 interface with MME 404.

As before, the mobile device (not shown) may initially be wirelesslyconnected to the base station 400 serving the source cell. As isconventional, the mobile device performs measurements of the strength ofany signals received from the source cell and neighbouring cells andperiodically sends a report (not shown) to the source cell 400 forprocessing.

The base station 400 serving the source cell, or a processor coupled tothat base station 400, analyses the report and evaluates whether themobile device should continue to be served by the source cell, orwhether it would be better served by a neighbouring cell.

Once it is determined that the mobile device might be better served by aneighbouring cell, the source base station 400 sends a HANDOVER REQUESTmessage 408 to the first target base station 402 directly, for instancevia an X2 link. The first target base station will reserve the necessaryresources, such as radio bearers and the C-RNTI, which are indicated bythe source base station 400. The first target base station will thensend a HANDOVER REQUEST ACKNOWLEDGE message 410 to the source basestation 400, for instance via an X2 link.

At the same time, the source base station 400 sends a HANDOVER REQUIREDmessage 412 via an S1 interface to the MME 404. Upon receipt of theHANDOVER REQUIRED message 412 from the source base station 400, the MMEforwards a HANDOVER REQUEST message 414 to the second target basestation 406. The second target base station 406 will reserve thenecessary resources, such as radio bearers and the C-RNTI, which areindicated by the source base station 400. The second target base station406 then sends a HANDOVER REQUEST ACKNOWLEDGE 416 message to the MME 404and the MME 404 will then send a HANDOVER COMMAND 418 to the source basestation.

In the embodiment of FIG. 4, assume that the mobile device attempts tohandover to the first target base station 402, but fails. Assume alsothat the mobile device then attempts to handover to the secondtarget-base station 406, and succeeds.

Once the mobile device has been identified in the second target basestation, the second target base station will send a HANDOVER NOTIFYmessage 422 to the MME, which will be forwarded 424 to the source cell.Of course, if the mobile device had succeeded in handing over to thefirst target base station, a HANDOVER NOTIFY message would have beensent from the first target base station to the source cell via the X2link.

Once the UE succeeded handover to one of the target cells, the reservedresource of the other candidate cells will be released. The release maybe explicitly signalled such as by a RELEASE RESOURCES message 420which, in the case of the method shown in FIG. 4, is sent from thesecond target base station to the first target base station.Alternatively, the release may be triggered by expiry of timer startedwhen the resource is initially reserved or the source base station 400may send the message 420 to the first base station 402.

The aforementioned methods may involve a certain amount of processing tobe carried out in base stations. For example, the source base stationmay have to transmit data to multiple target cells, all of which mayprocess that information and, optional, reserve and subsequentlyrelinquish resources. An alternative method is disclosed, with referenceto FIG. 10, which reduces the processing required by the base stations.

In the alternative method, once a source base station optionallydetermines that a mobile device should undergo a handover procedure, itmay provide that mobile device with a list candidate target cells, usingany of the techniques described above. Optionally, this list can be inpriority order, but this is not essential.

As shown in FIG. 10, the mobile device may receive 1002 the list ofcandidate target cells with the handover instructions as with any of themethods described above. As with the methods described previously, themobile device will then cease communication 1004 with the source celland attempt to handover 1006 to the first target cell in the pluralityof target cells in the handover message. If handover is successful 1008,the mobile device will commence communication 1010 with the first targetcell. If handover is unsuccessful 1008, the mobile device operatesslightly differently. Rather than attempt to handover to one or more ofthe plurality of further target cells when handover to the first or asubsequent target cell fails, the mobile device may instead attempt toperform a cell selection operation in an RRC Connection ReestablishmentProcedure 1012 using the list of candidate target cells received in thehandover instructions (rather than attempt to perform Stored InformationCell Selection or Initial Cell Selection in accordance with TS36.304, asdescribed above). This alternative method reduces the network load, suchas on X2 and S1 interfaces, and also speeds up cell selection.Additionally, this alternative method increases successfulreestablishment of a mobile device and may result in the mobile deviceremaining in an RRC_CONNECTED state without terminating existingtelecommunication connections.

Optionally, the mobile device may check the quality of a target cell itselects, prior to attempting to connect to it. A first optional way inwhich this check may be performed is as follows. The mobile device maycompare the signal strength and quality of the selected target cell witha threshold, or with another cell such as the strongest cell from whichit receives a signal. If the difference in the signal strength andquality is less than a predetermined signal level and qualitythresholds, the mobile device may choose to select the listed cell. Ifthe difference in the signal strength and quality is more than thepredetermined signal level and quality thresholds, the mobile device maychoose to select the strongest cell. Alternatively, if none of thelisted cells satisfy the required threshold, the strongest cell may beselected. Alternatively, if multiple listed cells satisfy the requiredthreshold, the cell with the least difference may be selected.

In one variant of the alternative method, the physical cell identity andthe frequency of each prepared target cell are provided in aPreparedTargetCellInformation list as a new information element in theRRC Connection Reconfiguration message sent by the source base station.Upon detection of a first or subsequent handover failure, the mobiledevice may perform a cell selection operation for an RRC connectionreestablishment procedure.

If the mobile device identifies a PreparedTargetCellInformation list inthe message sent by the source base station, the mobile device mayconsiders each target cell in the list as a candidate for cellselection, instead of performing the Stored Information Cell Selectionor Initial Cell Selection procedures specified in TS36.304.

If desired, the mobile device may perform Stored Information CellSelection or Initial Cell Selection procedures after considering orselecting one or more of the target cells in thePreparedTargetCellInformation list. Moreover, the mobile device mayselect the first cell from the PreparedTargetCellInformation list andstored information (or vice versa) which meets pre-defined cellselection criteria including at least one of received signal level andsignal quality. The mobile device may prioritise thePreparedTargetCellInformation list over the stored information.Alternatively the mobile device may consider all target cells in thePreparedTargetCellInformation list and stored information and select thebest target cell specified therein according to pre-defined cellselection criteria including at least one of received signal level andsignal quality.

In a further variant of the alternative method, the source base stationmay indicate at least one of minimum received signal level and minimumsignal quality to be applied to each target cell or all of the targetcells in the PreparedTargetCellInformation list. In this case, themobile device information received from the source base station may beused in cell selection processes described above.

If desired, the minimum received signal level indicated in the list maybe configured to be higher than that broadcast in the system informationand the minimum signal quality indicated in the list may be configuredto be higher than that broadcast in system information. This allows fora more robust reestablishment procedure.

Alternatively, the minimum received signal level indicated in the listmay be configured to be lower than that broadcast in the systeminformation and the minimum signal quality indicated in the list may beconfigured to be lower than that broadcast in system information. Thisallows for a faster reestablishment procedure.

An example specification of an entirely new prepared target cellinformation list suitable for putting the alternative method into effectis given below.

*** preparedTargetCellInfoList ::= SEQUENCE (SIZE (1..maxCells)) OFpreparedTargetCellInfo preparedTargetCellInfo ::= SEQUENCE {targetPhysCellId PhysCellId, carrierFreq CarrierFreqEUTRA OPTIONAL, --Need OP -- First alternative diffRxLev Q-RxLevmin OPTIONAL, -- Need OP-- Second alternative q-RxLevMin Q-RxLevmin OPTIONAL, -- Need OPq-QualMin Q-QualMin OPTIONAL  -- Need OP } ***

If the aforementioned methods are to be employed in a heterogeneousnetwork, in which a plurality of small cells served by comparatively lowpowered base stations is used along with macro cells, it may bedesirable to minimise interference. Optionally, this may be done byestablishing an Enhanced Physical Downlink Control Chanel (EPDCCH) whichis transmitted in specific resource blocks. If a target cell for use ina handover procedure is configured with EPDCCH, the handover commandsent by the source base station may also include EPDCCH configuration,for example the resource blocks to which EPDCCH is mapped, along with areference signal. The target base station may utilize EPDCCH in handoverprocedure or reestablishment procedure in order to increase successratio and minimise interference.

It will be appreciated that the methods described above may beimplemented by a computer readable medium such as memory 214 in thenetwork component 202 in FIG. 2. The memory 214 has computer readableinstructions stored thereon. The instructions are adapted, when executedby the processor 204 of the network component 202, to cause theprocessor 204 to generate handover information for use in any of thehandover procedures described above.

It will also be appreciated that the methods described above may beimplemented by a computer readable medium such as memory 308 in themobile device 300 in FIG. 3. The memory 308 has computer readableinstructions stored thereon. The instructions are adapted, when executedby the processor 302 of the mobile device 300, to cause the processor302 to process handover information for use in any of the handoverprocedures described above.

It will be appreciated that the aforementioned devices and methods havebeen provided as examples of ways in which the present invention may beput into practice and should not be understood as limiting the scope ofthe invention which is defined by the appended claims.

The following is a non-exhaustive list of embodiments which may or maynot be claimed.

-   1. A method in a network component for use in a cellular network,    the method comprising:    -   transmitting handover information from the network component to        a mobile device;    -   wherein the handover information comprises information including        information of a plurality of target cells with which the mobile        device may subsequently communicate.-   2. The method of embodiment 1, wherein the mobile device is    connected to a source cell when receiving the handover information    transmitted from the network component and is not connected to any    one of the plurality of target cells which are different to the    source cell.-   3. The method of embodiment 0 or embodiment 2, wherein the network    component is in wireless communication with the mobile device prior    to the transmission of handover information of the plurality of    target cells.-   4. The method of any preceding embodiment, further comprising, prior    to the step of transmitting handover information:    -   receiving at the network component at least one communication        parameter of the existing communication with the mobile device.-   5. The method of any preceding embodiment, further comprising, prior    to the step of transmitting handover information:    -   receiving at the networking component at least one communication        parameter of at least one candidate target cell transmitted from        the mobile device; and    -   determining, by the network component, based on the at least one        communication parameter, whether to transmit the handover        information, and only transmitting the handover information if        said determination is positive.-   6. The method of any preceding embodiment, further comprising    initiating a resource allocation procedure of the plurality of    target cells, wherein the resource allocation procedure comprises:    -   communicating directly with one or more network components of        the plurality of target cells to reserve resources of said one        or more network components of the plurality of target cells for        the mobile device; or    -   communicating with one or more network components of the        plurality of target cells via a control network component to        reserve resources of said one or more network components of the        plurality of target cells for the mobile device.-   7. The method of embodiment 6, further comprising, after the mobile    device has initiated communication with one of the plurality of    target cells, instructing release of resources of each of the one or    more network components of the plurality target cells other than the    network component with which the mobile device is in communication.-   8. A method in a mobile device for use in a cellular network, the    method comprising:    -   receiving handover information at the mobile device from a        source cell of the cellular network,    -   wherein the handover information comprises information including        information of a plurality of target cells with which the mobile        device may subsequently communicate.-   9. The method of embodiment 8, wherein the mobile device is    connected to the source cell when receiving the handover information    and is not connected to any one of the plurality of target cells    which are different to the source cell.-   10. The method of embodiment 8 or embodiment 9, further comprising    the mobile device, after receiving the handover information:    -   ceasing communication with the source cell; and    -   attempting to connect to a first target cell, being one of the        plurality of target cells.-   11. The method of embodiment 10, further comprising the mobile    device determining which one of the plurality of target cells is to    be the first target cell.-   12. The method of any of embodiments 8 to 11, wherein the mobile    device determines a priority order for attempting connection to the    plurality of target cells.-   13. The method of embodiment 12, further comprising the mobile    device attempting to connect to a first target cell, being one of    the plurality of target cells, and on a failure to connect to the    first target cell, the mobile device attempting to connect to a    second target cell, being the next target cell after the first    target cell specified according to the priority order.-   14. The method of embodiment 13, wherein a failure to connect is    defined by one or more of the following events detectable by the    mobile device: a communication synchronization failure of the mobile    device with the first target cell; a failure of the mobile device to    receive a master information block (MIB) of the first target cell; a    failure of the mobile device to receive a system information block    (SIB) of the first target cell; a random access failure in    connecting to the first target cell; a failure to apply a given    configuration required by the first target cell, such as a security    configuration.-   15. The method of any of embodiments 8 to 14, further comprising,    prior to the step of receiving handover information:    -   determining by the mobile device at least one communication        parameter of existing communication of the source cell; and    -   transmitting said at least one communication parameter of the        existing communication from the mobile device to the source        cell.-   16. The method of any of embodiments 8 to 15, further comprising,    prior to the step of receiving handover information:    -   determining by the mobile device at least one communication        parameter of at least one candidate target cell; and    -   transmitting said at least one communication parameter of said        at least one candidate target cell from the mobile device to the        source cell.-   17. The method of any of embodiments 8 to 16, further comprising,    after handover failure, the mobile device performing a    reestablishment procedure comprising attempting to connect to one of    the plurality of target cells.-   18. The method of embodiment 17, when dependent on any one of    embodiments 11 to 14, further comprising, after handover failure,    the mobile device performing a reestablishment procedure comprising    attempting to connect to the first target cell, being one of the    plurality of target cells, and on a failure to connect to the first    target cell, the mobile device attempting to connect to a second    target cell, being the next target cell after the first target cell    specified according to the priority order.-   19. The method of preceding embodiment, wherein the handover    information is sufficient to enable the mobile device to perform a    handover operation to a target cell.-   20. The method of any preceding embodiment, wherein the handover    information defines a priority order of the target cells.-   21. The method of any preceding embodiment, wherein the handover    information comprises:    -   a target frequency value or range for communicating with each        target cell; and/or    -   access parameters for each target cell.-   22. The method of preceding embodiment, wherein the handover    information comprises communication parameters of each target cell    sufficient for the mobile device to attempt to initiate    communication with each target cell without requiring prior    coordination of each target cell for communicating with the mobile    device.-   23. The method of any preceding embodiment, wherein the handover    information comprises cell identification information.-   24. The method of embodiment 23, wherein the handover information    comprises communication parameters of a first target cell sufficient    for the mobile device to attempt to initiate communication with the    first target cell without requiring prior coordination of the target    cells for communicating with the mobile device, and further    comprises cell identification information for each subsequent target    cell.-   25. The method of embodiment 24, wherein the handover information    comprises only cell information, such as a cell identification, for    each subsequent target cell.-   26. The method of any one of embodiments 0 to 21, wherein the    handover information comprises communication parameters of at least    one target cell sufficient for the mobile device to initiate    communication with a network component via the at least one target    cell without requiring prior coordination of the target cells for    communicating with the mobile device, wherein the handover    information further comprises communication parameters of additional    target cells comprising, or consisting only of, differences between    required communication parameters of the additional target cells and    the previously-transmitted communication parameters of the at least    one target cell.-   27. The method of any one of the preceding embodiments, wherein the    handover information is transmitted in a radio resource control    (RRC) connection reconfiguration message transmitted to the mobile    device.-   28. A network component for use in a cellular network, the network    having a plurality of cells, the network component comprising:    -   a processing unit configured to generate handover information;        and    -   a transmitter configured to transmit the handover information to        a mobile device,    -   wherein the handover information comprises information including        information of a plurality of target cells with which the mobile        device may subsequently communicate.-   29. The network component of embodiment 28, wherein the processing    unit is further adapted to receive from the mobile device at least    one communication parameter of the existing communication with the    mobile device.-   30. The network component of embodiment 28 or embodiment 29, wherein    the processing unit is further configured to:    -   receive at least one communication parameter of at least one        candidate target cell transmitted from the mobile device;    -   determine, based on the at least one communication parameter,        whether to transmit the handover information; and    -   transmit the handover information if said determination is        positive.-   31. The network component of any of embodiments 28 to 30, wherein    the processing unit is further configured to initiate a resource    allocation procedure of the plurality of target cells by virtue of    being configured to:    -   communicate directly with network components of the plurality of        target cells and reserve resources of the network components of        the plurality of target cells for the mobile device; or    -   communicate with the network components of the plurality of        target cells via a control network component and reserve        resources of the network components of the plurality of target        cells for the mobile device.-   32. The network component of embodiment 31, wherein the processing    unit is further configured to instruct release of resources of each    of the network components of the plurality target cells other than    the network component with which the mobile device is in    communication.-   33. A mobile device for communicating in a cellular network, the    mobile device comprising:    -   a receiver configured to receive handover information; and    -   a processing unit adapted to process the handover information,    -   wherein the handover information comprises information including        information of a plurality of target cells with which the mobile        device may subsequently communicate.-   34. The mobile device of embodiment 33, wherein the processing unit    is further configured to cease communication with a source cell of    the plurality of cells upon receipt of the handover communication;    and initiate communication with one of the plurality of target    cells.-   35. The mobile device of embodiment 33 or embodiment 34, wherein the    processing unit is further configured to connect to a first target    cell, being one of the plurality of target cells, and communicate    with said first target cell.-   36. The mobile device of embodiment 35, wherein the processing unit    is further configured to determine which one of the plurality of    target cells is to be the first target cell.-   37. The mobile device of any of embodiments 33 to 36, wherein the    processing unit is further configured to determine a priority order    for attempting connection to a cell of the plurality of target    cells.-   38. The mobile device of embodiment 37, wherein the processing unit    is further configured to attempt to connect to the first target    cell, being one of the plurality of target cells, and upon failing    to connect to the first target cell, attempt to connect to a second    target cell, being the next target cell after the first target cell    specified according to the priority order.-   39. The mobile device of embodiment 38, wherein the processing unit    is further configured to connect to the second target cell, being    one of the plurality of target cells, and communicate with said    second target cell.-   40. The mobile device of any of embodiments 33 to 39, wherein the    processing unit is further configured to determine at least one    communication parameter of existing communication with the source    cell; and transmit said at least one communication parameter of the    existing communication to the source cell.-   41. The mobile device of any of embodiments 33 to 40, wherein the    processing unit is further configured to:    -   determine at least one communication parameter of at least one        candidate target cell; and    -   transmit said at least one communication parameter of said at        least one candidate target cell to the source cell.-   42. The mobile device of any of embodiments 33 to 41, wherein the    processing unit is further configured to perform a reestablishment    procedure comprising attempting to connect to one of the plurality    of target cells.-   43. The mobile device of any of embodiments 37 to 42, wherein the    processing unit is further configured to perform a reestablishment    procedure comprising attempting to connect to the first target cell,    being one of the plurality of target cells, and on failing to    connect to the first target cell, attempting to connect to a second    target cell, being the next target cell after the first target cell    specified according to the priority order.-   44. A computer readable medium having computer readable instructions    stored thereon, the instructions executable by a processor to cause    the processor to generate handover information for use in a handover    procedure of a mobile device operating within a cellular-based    communications network, the handover information comprising    information of a plurality of target cells with which the mobile    device can subsequently communicate.-   45. A computer readable medium having computer readable instructions    stored thereon, the instructions executable a processor to cause the    processor to process handover information for use in a handover    procedure of a mobile device operating within a cellular network    having a plurality of cells, the handover information comprising    information of a plurality of target cells with which the mobile    device may subsequently communicate.-   46. A method in a mobile device for use in a cellular network, the    method comprising:    -   commencing a radio resource control (RRC) connection        reestablishment procedure comprising performing a cell selection        operation wherein one or more target cells which the mobile        device may select for re-establishment are specified in handover        information previously received at the mobile device.-   47. The method of embodiment 46, further comprising, prior to the    step of commencing a radio resource control (RRC) connection    reestablishment procedure, receiving the handover information at the    mobile device.-   48. The method of embodiment 46 or embodiment 47, further    comprising, prior to the step of commencing a radio resource control    (RRC) connection reestablishment procedure, the mobile device    attempting to connect to a first cell.-   49. The method of embodiment 48, further comprising the mobile    device failing to connect to the first cell, wherein the mobile    device selects one or more target cells in the cell selection    operation which is not the first cell.-   50. The method of embodiment 48 or embodiment 49, wherein the first    cell is a target cell specified in the handover information.-   51. The method of any of embodiments 46 to 50, wherein the handover    information comprises information of a plurality of target cells    with which the mobile device may subsequently communicate.-   52. The method of embodiment 51, further comprising, prior to the    step of commencing a radio resource control (RRC) connection    reestablishment procedure, the mobile device attempting to connect    to a first target cell, being one of the plurality of target cells.-   53. The method of any of embodiments 46 to 52, wherein the handover    information is received in a radio resource control (RRC) connection    reconfiguration message transmitted to the mobile device.-   54. The method of any of embodiments 46 to 53, wherein the step of    commencing a radio resource control (RRC) connection reestablishment    procedure occurs upon or after handover failure.-   55. The method of any of embodiments 46 to 54, further comprising    selecting a cell for reestablishment.-   56. The method of embodiment 55 further comprising the mobile device    determining which one of a plurality of cells including one or more    target cells specified in the handover information and one or more    cells not specified in the handover information is to be the first    cell it selects for reestablishment.-   57. The method of embodiment 55 or embodiment 56, wherein the mobile    device determines a priority order for the plurality of target cells    to be selected for reestablishment.-   58. The method of embodiment 57, further comprising the mobile    device selecting a first cell, being one of the plurality of cells,    and on a failure to connect to the first cell, the mobile device    attempting to connect to a second cell, being the next cell after    the first cell specified according to the priority order.-   59. The method of any of embodiments 46 to 58, wherein the mobile    device prioritises selecting one or more target cells specified in    the handover information over other cells.-   60. The method of any one of embodiments 55 to 59, further    comprising:    -   determining, by the mobile device, at least one signal parameter        of one or more target cells specified in the handover        information;        wherein the cell selected for reestablishment is a target cell        specified in the handover information if the determined at least        one signal parameter of the one or more target cells is greater        than a predetermined threshold.-   61. The method of any of embodiments 55 to 60, further comprising:    -   determining, by the mobile device, at least one signal parameter        of a cell not specified in the handover information; and    -   comparing the at least one signal parameter with at least one        signal parameter of one or more target cells specified in the        handover information.-   62. The method of embodiment 61, wherein the cell selected for    reestablishment is a target cell specified in the handover    information if:    -   the difference between:        -   a) the at least one signal parameter of the one or more            target cells specified in the handover information, and        -   b) the at least one signal parameter of the cell not            specified in the handover information,    -   is less than a predetermined threshold.-   63. The method of embodiment 62, wherein the cell selected for    reestablishment is the target cell specified in the handover    information having the at least one signal parameter which is    closest to the at least one signal parameter of the cell not    specified in the handover information.-   64. The method of any one of embodiments 61 to 63, wherein at least    one signal parameter includes one or more of signal quality and    signal strength.-   65. The method of any of embodiments 46 to 54, wherein the handover    information comprises a cell identification for the one or more each    target cell.-   66. The method of any of embodiments 46 to 65, wherein the handover    information comprises only a cell identification for the one or more    each target cell.-   67. A method in a network component for use in a cellular network,    the method comprising:    -   transmitting handover information for use in a reestablishment        procedure from the network component to a mobile device;    -   wherein the handover information comprises information of a        target cell with which the mobile device may subsequently        communicate.-   68. The method of embodiment 67, wherein the information comprises    information of a plurality of target cells with which the mobile    device may subsequently communicate.-   69. The method of embodiment 67 or embodiment 68, wherein the    information is transmitted in a radio resource control (RRC)    connection reconfiguration message.-   70. The method of any one of embodiments 67 to 69, wherein for at    least one target cell specified in the handover information, the    handover information further specifies a predetermined threshold    indicating the maximum permissible difference between at least one    signal parameter of the said at least one target cell specified in    the handover information and at least one signal parameter of a cell    not specified in the handover information.-   71. The method of embodiment 70, wherein the handover information    further specifies that:    -   if the difference between:        -   a) the at least one signal parameter of the said at least            one target cell specified in the handover information, and        -   b) the at least one signal parameter of the cell not            specified in the handover information,    -   is less than a predetermined threshold, the mobile device should        select the said at least one target cell specified in the        handover information.-   72. The method of any one of embodiments 70 to 71, wherein at least    one signal parameter includes one or more of signal quality and    signal strength.-   73. The method of any one of embodiments 67 to 72, wherein the    handover information comprises a cell identification for the at    least one target cell.-   74. The method of any one of embodiments 67 to 73, wherein the    handover information comprises only a cell identification for the at    least one target cell.-   75. A mobile device for communicating in a cellular network, the    mobile device comprising:    -   a receiver configured to receive handover information from one        of a plurality of cells; and    -   a processing unit adapted to process the handover information;    -   wherein the processor is adapted to commence a radio resource        control (RRC) connection reestablishment procedure and perform a        cell selection operation wherein one or more target cells which        the mobile device may select for re-establishment are specified        in handover information previously received at the mobile        device.-   76. The mobile device of embodiment 75, wherein the processing unit    is configured to perform the steps of any one of the methods in    embodiments 476 to 66.-   77. A network component for use in a cellular network, the network    having a plurality of cells, the network component comprising:    -   a processing unit configured to generate handover information        for use in a radio resource control (RRC) connection        reestablishment procedure;    -   a transmitter configured to transmit the handover information to        a mobile device,    -   wherein the handover information comprises information of a        target cell with which the mobile device may subsequently        communicate.-   78. The network component of embodiment 77, wherein the processing    unit is configured to perform the steps of any one of the methods in    embodiments 68 to 74.-   79. A computer readable medium having computer readable instructions    stored thereon, the instructions executable by a processor to cause    the processor to process handover information for use in a radio    resource control (RRC) connection reestablishment procedure of a    mobile device operating within a cellular network.-   80. The computer readable medium of embodiment 79, further    comprising computer readable instructions executable by a processor    to perform the steps of any one of embodiments 47 to 66.-   81. A computer readable medium having computer readable instructions    stored thereon, the instructions executable by a processor to cause    the processor to generate handover information for use in a radio    resource control (RRC) connection reestablishment procedure, wherein    the handover information comprises information of a target cell with    which the mobile device may subsequently communicate.-   82. The computer readable medium of embodiment 81, further    comprising computer readable instructions executable by a processor    to perform the steps of any one of embodiments 68 to 74.

1. A method in a network component for use in a cellular network, themethod comprising: transmitting handover information from the networkcomponent to a mobile device; wherein the handover information comprisesinformation including information of a plurality of target cells withwhich the mobile device may subsequently communicate.
 2. The method ofclaim 1, wherein the mobile device is connected to a source cell whenreceiving the handover information transmitted from the networkcomponent and is not connected to any one of the plurality of targetcells which are different to the source cell.
 3. The method of claim 1,wherein the network component is in wireless communication with themobile device prior to the transmission of handover information of theplurality of target cells.
 4. The method of claim 1, further comprising,prior to the step of transmitting handover information: receiving at thenetwork component at least one communication parameter of the existingcommunication with the mobile device.
 5. The method of claim 1, furthercomprising, prior to the step of transmitting handover information:receiving at the networking component at least one communicationparameter of at least one candidate target cell transmitted from themobile device; and determining, by the network component, based on theat least one communication parameter, whether to transmit the handoverinformation, and only transmitting the handover information if saiddetermination is positive.
 6. The method of claim 1, further comprisinginitiating a resource allocation procedure of the plurality of targetcells, wherein the resource allocation procedure comprises:communicating directly with one or more network components of theplurality of target cells to reserve resources of said one or morenetwork components of the plurality of target cells for the mobiledevice; or communicating with one or more network components of theplurality of target cells via a control network component to reserveresources of said one or more network components of the plurality oftarget cells for the mobile device.
 7. The method of claim 6, furthercomprising, after the mobile device has initiated communication with oneof the plurality of target cells, instructing release of resources ofeach of the one or more network components of the plurality target cellsother than the network component with which the mobile device is incommunication.
 8. The method of claim 1, wherein the handoverinformation is sufficient to enable the mobile device to perform ahandover operation to a target cell.
 9. The method of claim 1, whereinthe handover information defines a priority order of the target cells.10. The method of claim 1, wherein the handover information comprises: atarget frequency value or range for communicating with each target cell;and/or access parameters for each target cell.
 11. The method of claim1, wherein the handover information comprises communication parametersof each target cell sufficient for the mobile device to attempt toinitiate communication with each target cell without requiring priorcoordination of each target cell for communicating with the mobiledevice.
 12. The method of claim 1, wherein the handover informationcomprises cell identification information.
 13. The method of claim 12,wherein the handover information comprises communication parameters of afirst target cell sufficient for the mobile device to attempt toinitiate communication with the first target cell without requiringprior coordination of the target cells for communicating with the mobiledevice, and further comprises cell identification information for eachsubsequent target cell.
 14. The method of claim 13, wherein the handoverinformation comprises only cell information, such as a cellidentification, for each subsequent target cell.
 15. The method of claim14, wherein the handover information comprises communication parametersof at least one target cell sufficient for the mobile device to initiatecommunication with a network component via the at least one target cellwithout requiring prior coordination of the target cells forcommunicating with the mobile device, wherein the handover informationfurther comprises communication parameters of additional target cellscomprising, or consisting only of, differences between requiredcommunication parameters of the additional target cells and thecommunication parameters of the at least one target cell.
 16. The methodof claim 1, wherein the handover information is transmitted in a radioresource control (RRC) connection reconfiguration message transmitted tothe mobile device.
 17. A method in a mobile device for use in a cellularnetwork, the method comprising: receiving handover information at themobile device from a source cell of the cellular network, wherein thehandover information comprises information including information of aplurality of target cells with which the mobile device may subsequentlycommunicate.
 18. The method of claim 17, wherein the mobile device isconnected to the source cell when receiving the handover information andis not connected to any one of the plurality of target cells which aredifferent to the source cell.
 19. The method of claim 17, furthercomprising the mobile device, after receiving the handover information:ceasing communication with the source cell; and attempting to connect toa first target cell, being one of the plurality of target cells.
 20. Themethod of claim 19, further comprising the mobile device determiningwhich one of the plurality of target cells is to be the first targetcell.
 21. The method of claim 17, wherein the mobile device determines apriority order for attempting connection to the plurality of targetcells.
 22. The method of claim 21, further comprising the mobile deviceattempting to connect to the first target cell, being one of theplurality of target cells, and on a failure to connect to the firsttarget cell, the mobile device attempting to connect to a second targetcell, being the next target cell after the first target cell specifiedaccording to the priority order.
 23. The method of claim 22, wherein afailure to connect is defined by one or more of the following eventsdetectable by the mobile device: a communication synchronization failureof the mobile device with the first target cell; a failure of the mobiledevice to receive a master information block (MIB) of the first targetcell; a failure of the mobile device to receive a system informationblock (SIB) of the first target cell; a random access failure inconnecting to the first target cell; a failure to apply a givenconfiguration required by the first target cell, such as a securityconfiguration.
 24. The method of claim 17, further comprising, prior tothe step of receiving handover information: determining by the mobiledevice at least one communication parameter of existing communication ofthe source cell; and transmitting said at least one communicationparameter of the existing communication from the mobile device to thesource cell.
 25. The method of claim 17, further comprising, prior tothe step of receiving handover information: determining by the mobiledevice at least one communication parameter of at least one candidatetarget cell; and transmitting said at least one communication parameterof said at least one candidate target cell from the mobile device to thesource cell.
 26. The method of claim 20, further comprising, afterhandover failure, the mobile device performing a reestablishmentprocedure comprising attempting to connect to one of the plurality oftarget cells.
 27. The method of claim 26, further comprising, afterhandover failure, the mobile device performing a reestablishmentprocedure comprising attempting to connect to the first target cell,being one of the plurality of target cells, and on a failure to connectto the first target cell, the mobile device attempting to connect to asecond target cell, being the next target cell after the first targetcell specified according to the priority order.
 28. The method of claim17, wherein the handover information is sufficient to enable the mobiledevice to perform a handover operation to a target cell.
 29. The methodof claim 17, wherein the handover information defines a priority orderof the target cells.
 30. The method of claim 17, wherein the handoverinformation comprises: a target frequency value or range forcommunicating with each target cell; and/or access parameters for eachtarget cell.
 31. The method of claim 17, wherein the handoverinformation comprises communication parameters of each target cellsufficient for the mobile device to attempt to initiate communicationwith each target cell without requiring prior coordination of eachtarget cell for communicating with the mobile device.
 32. The method ofclaim 17, wherein the handover information comprises cell identificationinformation.
 33. The method of claim 17, wherein the handoverinformation comprises communication parameters of a first target cellsufficient for the mobile device to attempt to initiate communicationwith the first target cell without requiring prior coordination of thetarget cells for communicating with the mobile device, and furthercomprises cell identification information for each subsequent targetcell.
 34. The method of claim 33, wherein the handover informationcomprises only cell information, such as cell identificationinformation, for each subsequent target cell.
 35. The method of claim17, wherein the handover information comprises communication parametersof at least one target cell sufficient for the mobile device to initiatecommunication with a network component via the at least one target cellwithout requiring prior coordination of the target cells forcommunicating with the mobile device, wherein the handover informationfurther comprises communication parameters of additional target cellscomprising, or consisting only of, differences between requiredcommunication parameters of the additional target cells and thepreviously-transmitted communication parameters of the at least onetarget cell.
 36. The method of claim 17, wherein the handoverinformation is transmitted in a radio resource control (RRC) connectionreconfiguration message transmitted to the mobile device.
 37. A networkcomponent for use in a cellular network, the network having a pluralityof cells, the network component comprising: a processing unit configuredto generate handover information; and a transmitter configured totransmit the handover information to a mobile device, wherein thehandover information comprises information including information of aplurality of target cells with which the mobile device may subsequentlycommunicate.
 38. The network component of claim 37, wherein theprocessing unit is further adapted to receive from the mobile device atleast one communication parameter of the existing communication with themobile device.
 39. The network component of claim 37, wherein theprocessing unit is further configured to: receive at least onecommunication parameter of at least one candidate target celltransmitted from the mobile device; determine, based on the at least onecommunication parameter, whether to transmit the handover information;and transmit the handover information if said determination is positive.40. The network component of claim 37, wherein the processing unit isfurther configured to initiate a resource allocation procedure of theplurality of target cells by virtue of being configured to: communicatedirectly with network components of the plurality of target cells andreserve resources of the network components of the plurality of targetcells for the mobile device; or communicate with the network componentsof the plurality of target cells via a control network component andreserve resources of the network components of the plurality of targetcells for the mobile device.
 41. The network component of claim 40,wherein the processing unit is further configured to instruct release ofresources of each of the network components of the plurality targetcells other than the network component with which the mobile device isin communication.
 42. A mobile device for communicating in a cellularnetwork, the mobile device comprising: a receiver configured to receivehandover information; and a processing unit adapted to process thehandover information, wherein the handover information comprisesinformation including information of a plurality of target cells withwhich the mobile device may subsequently communicate.
 43. The mobiledevice of claim 42, wherein the processing unit is further configured tocease communication with a source cell of the plurality of cells uponreceipt of the handover communication; and initiate communication withone of the plurality of target cells.
 44. The mobile device of claim 42,wherein the processing unit is further configured to connect to a firsttarget cell, being one of the plurality of target cells, and communicatewith said first target cell.
 45. The mobile device of claim 44, whereinthe processing unit is further configured to determine which one of theplurality of target cells is to be the first target cell.
 46. The mobiledevice of claim 42, wherein the processing unit is further configured todetermine a priority order for attempting connection to a cell of theplurality of target cells.
 47. The mobile device of claim 46, whereinthe processing unit is further configured to attempt to connect to thefirst target cell, being one of the plurality of target cells, and uponfailing to connect to the first target cell, attempt to connect to asecond target cell, being the next target cell after the first targetcell specified according to the priority order.
 48. The mobile device ofclaim 47, wherein the processing unit is further configured to connectto the second target cell, being one of the plurality of target cells,and communicate with said second target cell.
 49. The mobile device ofclaim 42, wherein the processing unit is further configured to determineat least one communication parameter of existing communication with thesource cell; and transmit said at least one communication parameter ofthe existing communication to the source cell.
 50. The mobile device ofclaim 42, wherein the processing unit is further configured to:determine at least one communication parameter of at least one candidatetarget cell; and transmit said at least one communication parameter ofsaid at least one candidate target cell to the source cell.
 51. Themobile device of claim 42, wherein the processing unit is furtherconfigured to perform a reestablishment procedure comprising attemptingto connect to one of the plurality of target cells.
 52. The mobiledevice of claim 46, wherein the processing unit is further configured toperform a reestablishment procedure comprising attempting to connect tothe first target cell, being one of the plurality of target cells, andon failing to connect to the first target cell, attempting to connect toa second target cell, being the next target cell after the first targetcell specified according to the priority order.
 53. A computer readablemedium having computer readable instructions stored thereon, theinstructions executable by a processor to cause the processor togenerate handover information for use in a handover procedure of amobile device operating within a cellular-based communications network,the handover information comprising information of a plurality of targetcells with which the mobile device can subsequently communicate.
 54. Acomputer readable medium having computer readable instructions storedthereon, the instructions executable a processor to cause the processorto process handover information for use in a handover procedure of amobile device operating within a cellular network having a plurality ofcells, the handover information comprising information of a plurality oftarget cells with which the mobile device may subsequently communicate.